The present invention relates to a process which comprises introducing a chelating group into a vinyl phenol polymer, such as a polyhydroxystyrene, (the reaction product hereinafter referred to as a Chelated Poly Vinyl Phenol--CPVP), by reacting a vinyl phenol polymer with a suitable diazonium salt of an aromatic amine, or substituted aromatic amine. Further, the present invention also relates to a process for producing a polymer which is insoluble in organic solvent systems (Condensed Substituted Poly Vinyl Phenol--CSPVP) by condensing a CPVP and formaldehyde to provide an organic solvent rigid CSPVP polymer. This polymer can then be ground to provide a particle size of, e.g. from about 200-400 mesh. The present invention also relates to a process for removing metal ions from such a CPVP or CSPVP to provide an ion exchange resin to remove metal ions from aqueous and non-aqueous systems, such as photoresist solutions or solutions of components for photoresist compositions.
Photoresist compositions are used in microlithorgraphy processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of a film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate substantially all of the solvent in the photoresist composition, and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.
Metal ion contamination has been a problem for a long time in the fabrication of high density integrated circuits and computer chips, often leading to increased defects, yield losses, degradation and decreased performance. In plasma processes, metal ions such as sodium and iron, when they are present in photoresists, can cause contamination especially during plasma stripping. However, these problems may be overcome to a substantial extent during the fabrication process. For example, by utilizing HCl gettering of the contaminants during a high temperature anneal cycle.
As semiconductor devices have become more sophisticated, these problems have become much more difficult to overcome. When silicon wafers are coated with a liquid positive photoresist and subsequently stripped off, such as with oxygen microwave plasma, the performance and stability of the semiconductor device is often seen to decrease. As the plasma stripping process is repeated, more degradation of the device frequently occurs. A primary cause of such problems has been found to be the metal contamination in the photoresist, particularly sodium and iron ions. Metal levels of less than 1.0 ppm in the photoresist have been found to adversely affect the properties of such semiconductor devices.